1. Field of the Invention
The present invention is broadly concerned with recovering and cleansing organic wastes from liquid slurries. More specifically it is a method of removing sand and soluble salts from the organic solids and concentrating and dewatering the solids to yield a low salt, high organic material that can be used as a peat substitute, growing media, fertilizer carrier, soil ammendment, composting material, or fuel for co-gen plants.
2. Description of the Prior Art
Many different organic wastes are produced each day. This invention is concerned with those that can be handled and pumped as a liquid, usually above 95% water and less than 5% suspended solids, hereinafter a "slurry". These slurries consist of a liquid (usually water), organic parts of plants, dissolved minerals (soluble salts) and sand and dirt contamination. When the slurry is mechanically screened or dried by evaporation, the salts and sand and dirt remain with the solids and limit the use and value of the solids. Examples of some slurries are trim and rejects from vegetable processing plants, peeling wastes from potato processors, offal from livestock slaughter plants, manure slurries from livestock and poultry producing facilities, distillers grains from alchohol plants and breweries. There have been many different attempts to dispose of these wastes such as livestock feed, landfill burial, soil application, biological degradation in lagoons, or just release to surface streams or lakes. Sand and dirt contamination may be high, limiting the use as livestock feeds or as a fuel source. Landfill burial of organic wastes with high soluble salts can cause ground water polution. Harmful salts limit the use as soil application. Biological degradation is difficult and costly due to high BOD (Biological Oxygen Demand). The desanding, desalting, and concentration of these wastes converts them into a usable form that can be used in many beneficial ways. The United States imports over 500,000 tons per year of sphagnum peat moss. Treated properly, organic wastes can be substituted for sphagnum peat moss in planting mixes. With soluble salts removed organic wastes can be used as soil ammendments, increasing organic matter and water holding capacity of the soil. They can be used for bedding in livestock and poultry production. A continual supply of low ash organic material is needed as fuel for electrical generation plants.
Solid separation from the slurry is normally attemped by passing the slurry over a screen. Organic wastes separated this way retain a high level of soluble salts, limiting their use in soils, feeds, fertilizers, or growing media. Screens continually plug up and become less efficient. Sand is separated as a part of the solid portion, limiting use as generation plant fuel and causing costly wear on equipment. U.S. Pat. No. 5,185,087 uses hydrocyclone with ruminant waste for concentrating, then allowing the solids to drain at will. The extent of salt removal is not controlled, water removal is not as complete as needed and sand contamination remains with the solids.